Metal oxides and semimetal oxides are commonly incorporated into semiconductor constructions. For instance, metal oxides and semimetal oxides can be utilized as dielectric materials in capacitor structures, and can be utilized as dielectric materials in other types of semiconductor devices.
One of the methods that has been developed for forming metal oxide materials and semimetal oxide materials involves the utilization of a metal chloride precursor (such as, for example, hafnium chloride, titanium chloride, zirconium chloride, etc.) or semimetal chloride precursor (such as, for example, silicon chloride) to form a metal-chloride-containing layer or semimetal-chloride-containing layer over a substrate surface. The metal-chloride-containing layer or semimetal-chloride-containing layer is then exposed to water to convert the metal chloride or semimetal chloride to metal oxide or semimetal oxide.
The formation of the metal-chloride-containing layer (or semimetal-chloride-containing layer) and conversion of the metal-chloride-containing layer (or semimetal-chloride-containing layer) to metal oxide (or semimetal oxide) can be accomplished by either atomic layer deposition (ALD) processes or chemical vapor deposition (CVD) processes.
ALD technology typically involves formation of successive atomic layers on a substrate. Such layers may comprise, for example, an epitaxial, polycrystalline, and/or amorphous material. ALD may also be referred to as atomic layer epitaxy, atomic layer processing, etc.
Described in summary, ALD includes exposing an initial substrate to a first chemical species to accomplish chemisorption of the species onto the substrate. Theoretically, the chemisorption forms a monolayer that is uniformly one atom or molecule thick on the entire exposed initial substrate. In other words, a saturated monolayer. Practically, as further described below, chemisorption might not occur on all portions of the substrate. Nevertheless, such an imperfect monolayer is still a monolayer in the context of this document. In many applications, merely a substantially saturated monolayer may be suitable. A substantially saturated monolayer is one that will still yield a deposited layer exhibiting the quality and/or properties desired for such layer.
The first species is purged from over the substrate and a second chemical species is provided to chemisorb onto the first monolayer of the first species. The second species is then purged and the steps are repeated with exposure of the second species monolayer to the first species. In some cases, the two monolayers may be of the same species. Also, a third species or more may be successively chemisorbed and purged just as described for the first and second species. It is noted that one or more of the first, second and third species can be mixed with inert gas to speed up pressure saturation within a reaction chamber.
Purging may involve a variety of techniques including, but not limited to, contacting the substrate and/or monolayer with a carrier gas and/or lowering pressure to below the deposition pressure to reduce the concentration of a species contacting the substrate and/or chemisorbed species. Examples of carrier gases include N2, Ar, He, Ne, Kr, Xe, etc. Purging may instead include contacting the substrate and/or monolayer with any substance that allows chemisorption byproducts to desorb and reduces the concentration of a species preparatory to introducing another species. A suitable amount of purging can be determined experimentally as known to those skilled in the art. Purging time may be successively reduced to a purge time that yields an increase in film growth rate. The increase in film growth rate might be an indication of a change to a non-ALD process regime and may be used to establish a purge time limit.
ALD is often described as a self-limiting process, in that a finite number of sites exist on a substrate to which the first species may form chemical bonds. The second species might only bond to the first species and thus may also be self-limiting. Once all of the finite number of sites on a substrate are bonded with a first species, the first species will often not bond to other of the first species already bonded with the substrate. However, process conditions can be varied in ALD to promote such bonding and render deposition which is not self-limiting. Accordingly, ALD may also encompass a species forming other than one monolayer at a time by stacking of a species, forming a layer more than one atom or molecule thick. The various aspects of the present invention described herein are applicable to any circumstance where ALD may be desired. It is further noted that local chemical reactions can occur during ALD (for instance, an incoming reactant molecule can displace a molecule from an existing surface rather than forming a monolayer over the surface). To the extent that such chemical reactions occur, they are generally confined within the uppermost monolayer of a surface.
Traditional ALD can occur within frequently-used ranges of temperature and pressure and according to established purging criteria to achieve the desired formation of an overall ALD layer one monolayer at a time. Even so, ALD conditions can vary greatly depending on the particular precursors, layer composition, deposition equipment, and other factors according to criteria known by those skilled in the art. Maintaining the traditional conditions of temperature, pressure, and purging minimizes unwanted reactions that may impact monolayer formation and quality of the resulting overall ALD layer. Accordingly, operating outside the traditional temperature and pressure ranges may risk formation of defective monolayers.
The general technology of chemical vapor deposition (CVD) includes a variety of more specific processes, including, but not limited to, plasma enhanced CVD and others. CVD is commonly used to form non-selectively a complete, deposited material on a substrate. One characteristic of CVD is the simultaneous presence of multiple species in the deposition chamber that react to form the deposited material. Such condition is contrasted with the purging criteria for traditional ALD wherein a substrate is contacted with a single deposition species that chemisorbs to a substrate or previously deposited species. An ALD process regime may provide a simultaneously contacted plurality of species of a type or under conditions such that ALD chemisorption, rather than CVD reaction occurs. Instead of reacting together, the species may chemisorb to a substrate or previously deposited species, providing a surface onto which subsequent species may next chemisorb to form a complete layer of desired material.
Under most CVD conditions, deposition occurs largely independent of the composition or surface properties of an underlying substrate. By contrast, chemisorption rate in ALD might be influenced by the composition, crystalline structure, and other properties of a substrate or chemisorbed species. Other process conditions, for example, pressure and temperature, may also influence chemisorption rate. Accordingly, observation indicates that chemisorption might not occur appreciably on portions of a substrate though it occurs at a suitable rate on other portions of the same substrate. Such a condition may introduce intolerable defects into a deposited material.
Regardless of whether ALD, CVD or a combination of ALD and CVD is utilized to form metal oxide or semimetal oxide, there can be difficulties associated with the metal oxide or semimetal oxide formation. One of the problems with conventional processes for forming metal oxide and semimetal oxide is that the processes frequently involve utilization of water as a reactant. The amounts of water utilized in such deposition processes can cause incorporation of OH groups in deposited films which degrade electrical performance of dielectric materials. In addition, water can be extremely difficult to remove from within a vacuum chamber. Water within a vacuum chamber can cause unwanted side reactions (such as corrosion) relative to semiconductor structures associated with a substrate exposed to the water, and relative to the interior regions of a reaction chamber. In light of the above-discussed problems, it is desired to develop new methods for formation of metal oxides and semimetal oxides.
Although the invention was motivated, at least in part, by a desire to alleviate the above-discussed problems associated with utilization of water in deposition processes, it is to be understood that the invention is not limited to such aspects.